1. Field of the Invention
The present invention relates to accelerometers and more particularly to rotational rate sensors.
2. Description of Related Art
Electrolytic tilt or rate sensors are known in the art. Electrolytic tilt sensors include devices that change their electrical properties as a result of the interface of the electrolyte with electrodes contained therein when tilted or moved. For example, known electrolytic tilt sensors may provide an output voltage proportional to the tilt angle, a phase indication of tilt direction and an acceleration associated with the tilt when the sensor is configured as part of an appropriate electrical circuit. In such an example, the output voltage derives from the impedance associated with the electrolyte (also referred to as the electrolytic fluid or solution) of the sensor, which is a function of the tilt of the electrolyte due to gravitational or other forces.
One of the difficulties in fabricating an inexpensive angular rate or rotation rate sensors is producing a device that is insensitive to the constant acceleration of gravity. The majority of rate sensors are either tuning fork-type devices sensing a relatively weak force (i.e., Coriolis effect) and thus not very sensitive, or gyroscopes (either rotating or fiber optic-based) that are large, consuming lots of power and are expensive.
Briefly, the invention includes a novel rate sensing device, more particularly, a toroid accelerometer. The accelerometer includes a housing having a fluid cavity completely or essentially completely filled with an electrolytic fluid (e.g., liquid). Within the housing and electrolytic fluid is disposed at least one excitation electrode and at least one ground electrode as well as at least one output electrode. Ordinarily the output electrode(s) are connected (exterior to the cavity) to a differential amplifier which is connected (also exteriorly) to a synchronous demodulator.
During operation, the accelerometer is fixedly mounted to an object of rate measure so that (upon movement of the object) the electrolytic fluid moves around within the fluid-filled housing cavity and a majority of the fluid ions are swept from the excitation electrode toward one of the output electrodes. A positive output signal is generated from such an output electrode (via the amplifier and demodulator) in one direction of rotation and a negative output signal generated for the opposite direction of rotation. Neutralization of the ions in the moving fluid occurs at a ground electrode so that no effect on the opposite output can occur. Other than the electrolytic fluid, the accelerometer advantageously has essentially no movable parts.
Such a sensing device is particularly effective for oil well tool rotation sensing, angular acceleration sensing for six-axis accelerometers, robotics sensing, control system feedback, video game input, pedometers, inertial navigation and steering wheel motion sensing.